Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance

by Alex Hutchinson

It turns out that, whether it’s heat or cold, hunger or thirst, or muscles screaming with the supposed poison of “lactic acid,” what matters in many cases is how the brain interprets these distress signals.

We now know that lactate from muscle and blood, once extracted from the body, combines with protons to produce lactic acid.

The importance of oxygen was confirmed the next year by Leonard Hill, a physiologist at the London Hospital Medical College, in the British Medical Journal.13 He administered pure oxygen to runners, swimmers, laborers, and horses, with seemingly astounding results. A marathon runner improved his best time over a trial distance of three-quarters of a mile by 38 seconds.

He ultimately made twenty-two attempts at the Channel crossing, all unsuccessful.)

If at first...

Crucially, they could still accelerate to faster speeds; however, their oxygen intake no longer followed. This plateau is your VO2max, a pure and objective measure of endurance capacity that is, in theory, independent of motivation, weather, phase of the moon, or any other possible excuse. Hill surmised that VO2max reflected the ultimate limits of the heart and circulatory system—a measurable constant that seemed to reveal the size of the “engine” an athlete was blessed with.

“A live donkey is better than a dead lion, isn’t it?” Shackleton had said to his wife when he returned to England.

In the final days of the record attempt, Van Deren’s feet were so beat up that she had to start each day by crawling along the trail until, thanks to the familiar numbing of endorphins, she could stand up and start putting weight on them.

First, the limits we encounter during exercise aren’t a consequence of failing muscles; they’re imposed in advance by the brain to ensure that we never reach true failure. And second, the brain imposes these limits by controlling how much muscle is recruited at a given effort level

In his view, the decision to speed up, slow down, or quit is always voluntary, not forced on you by the failure of your muscles. Fatigue, in other words, ultimately resides in the brain—an

caffeine pills are already one of the most widely used legal supplements among athletes—but

All three men, like the vast majority of the world’s best distance runners these days, were born, grew up, and train in the East African highlands along the Great Rift Valley, at elevations of at least 6,000 feet above sea level. The thin, oxygen-poor air at these heights makes running harder and triggers adaptations like an increase in the number of red blood cells available to shuttle oxygen from the lungs to working muscles. In fact, anyone born into this environment carries oxygen-sparing traits like enhanced lung volume with them for the rest of their lives.

In 2010, a team of researchers led by Alexis Mauger, who was then at the University of Exeter, in Britain, showed that giving well-trained cyclists 1,500 milligrams of acetaminophen—plain old Tylenol—boosted their performance in a 10-mile time trial by about 2 percent compared to when they were given a placebo.

The potential of tDCS to enhance learning, mood, motor function, and even (as we’ll see in Chapter 11) endurance has earned it a wave of hype in recent years. When directed at the brain’s motor cortex, it also has pain-suppressing properties, which is what Mauger and Marcora were interested in here.

“As soon as I get to the car, the boy is just screaming his head off, and I could tell he was in a lot of pain,” Boyle later recalled. So he lifted the car up. “Mister, mister, higher, higher!” Holtrust screamed. When it was high enough, Boyle yelled to the Camaro’s driver, who snapped out of a daze and pulled Holtrust out.

Between April and July 1940 alone, more than 35 million tablets of “Panzerschokolade” (tank chocolate) fueled the Blitzkrieg across Europe, spurring lasting rumors of a Nazi superpill that gave soldiers extraordinary powers. (The dark aftereffects of crystal meth became clearer over time, and German officials restricted its used in 1941, though it remained widely used until the end of the war—and stayed part of the East German army’s war chest until 1988.)

When Millet compared muscle fatigue following three hours of running to similar durations of cycling and cross-country skiing, he found that voluntary activation declined by 8 percent in running but didn’t change in cycling or skiing. The difference between these three activities? The impact forces in running cause microscopic damage that alters the properties of your leg muscles, unlike the two impact-free activities.

The Australian Olympic team brought ice baths to the sun-drenched 2004 games in Athens, so that athletes could plunge in shortly before their events.17 In 2008, they adopted a simpler and more practical approach, shipping seven slushie machines to Beijing and deploying them at the venues for track, cycling, soccer, triathlon, and several other sports. Just as the transformation of liquid water to vapor cools your skin when you sweat, the “phase change energy” of ice melting to water in your stomach provides an extra cooling boost beyond what you would get from simply drinking a cold drink.

Heat doesn’t act like a light switch that flicks your muscles off; in most real-world situations, as Tucker explained to me, it’s a dimmer switch, controlled by the brain for your own protection.

Gatorade isn’t just a rehydrator; its sugar also restocks the fuel stores that your muscles are burning through

But there was no further improvement when they drank more than they had chosen to in the first trial. Avoiding thirst, rather than avoiding dehydration, seems to be the most important key to performance.

This, in turn, helps to explain why a later study found that swallowing small mouthfuls of water—too small to make any difference to overall hydration levels—boosted exercise performance by 17 percent compared to rinsing the same amount of water in the mouth and then spitting it out.

Marathoners can handle 10 percent dehydration for a few hours. But that assumes you’re properly hydrated when you arrive at the start line—a factor that is, if anything, even more important than what you drink during exercise, according to Stephen Cheung’s research.

There are other sources of carbohydrate in the body; your liver, for example, can store 400 or 500 calories of glycogen for use throughout the body, compared to about 2,000 for fully loaded leg muscles. (That’s why it’s useful to eat a small breakfast a few hours before a morning marathon: while your muscles remain fully stocked, your liver glycogen gets depleted because it fuels your energy-hungry brain while you sleep.)

Neither man developed scurvy, thanks to the vitamin C contained in animal organs and other cuts. Stefansson’s worst moments came at the start of the experiment, when the investigators fed him only lean meat. In the Arctic, he had noted, the Inuit relished the fattiest parts of the animal, giving the leanest meat to the dogs. Once he switched to fattier cuts, so that about three-quarters of his calories came from fat, he was fine.

scientists have traditionally figured that 60 grams an hour (about 250 calories) is pretty much the maximum amount you can absorb during exercise.

if you combine two different types of carbohydrate—glucose and fructose, for example—they pass through the intestinal wall using two different cellular routes that can operate simultaneously, enabling you to absorb as much as 90 grams of carbohydrate per hour.26

In reality, as Volek’s data shows, we all use both. And given the complementary strengths and weaknesses of the two options—carbohydrate as a fast fuel with limited storage capability, fat as an inexhaustible but rate-limited alternative, it makes sense to aim for what Louise Burke, of the Australian Institute of Sport, calls “metabolic flexibility,” by maximizing both fuel pathways.

The answer, Tucker suggested, was Borg’s rating of perceived exertion, or RPE, which he described as “the conscious/verbal manifestation of the integration of these psychological and physiological cues.” Moreover, this effort rating climbs gradually as body temperature increases or carbohydrate stores decrease: it doesn’t just wait for the catastrophe; it anticipates it. Pacing, in Tucker’s formulation, is the process of comparing the effort you feel at any given point in a race to the effort you expect at that stage—an internal template that you develop and fine-tune from experience. If the start of a race feels like a 10 out of 20 effort on the Borg scale, and you expect to hit 20 by the end, then halfway through the race the effort should feel like a 15.

Subjectively, psychological tests showed that the BMX riders displayed greater awareness of bodily sensations, and the national team head coach noted improvements in their race performance. “Their body language is calmer in the gate,” the coach said. “They move their hands less on the bars, and they get out of the gate a little faster.”15

Even the humblest Kenyan runner, he noticed, wakes up every morning with the firm conviction that today, finally, will be his or her day. They run with the leaders because they think they can beat them, and if harsh reality proves that they can’t, they regroup and try again the next day. And that belief, fostered by the longstanding international dominance of generations of Kenyan runners, becomes a self-fulfilling prophecy.

Consider the purported benefits of a post-workout ice bath, which is supposed to ward off inflammation and hasten muscle recovery.5 Athletes at every level swear by them; researchers, meanwhile, have published hundreds of studies investigating their effects, with results that are ambiguous at best. If you ask athletes how sore they feel the day after a workout, ice baths seem to help; if you take blood tests to look for objective signs of reduced muscle damage, not so much.

The subjects were told they would receive various doses of caffeine before each trial, but they wouldn’t be told which dose they had received. As expected, the cyclists rode 1.3 percent faster when they thought they had received a moderate dose, 3.1 percent faster after a high dose, and 1.4 percent slower when they thought they got the placebo.10 In reality, all the pills were placebos. The performance boost, and associated changes in how much pain or effort they perceived during the rides, were entirely fueled by their own expectations.

“You have to teach athletes, somewhere in their careers, that they can do more than they think they can.”

which is why his super-workout consisted of five times a mile as hard as possible, followed by your coach telling you to do another at the same pace. “From this workout, you’ll learn forever that you’re capable of much more than you think,” he wrote. “It’s the most powerful lesson you can possibly learn in running.”

Why is it that world records in virtually every test of human endurance keep edging downward? You might think it’s our ever-advancing knowledge of training, nutrition, hydration, recovery and so on, along with fancy technologies like cryosaunas. But all of this knowledge and technology is applied with equal enthusiasm to nonhuman sports like horse and dog racing. The financial stakes in horse racing, thanks to legalized betting, dwarf those in human endurance racing. And sure enough, for the first half of the twentieth century, Thoroughbreds and humans got faster at roughly similar rates. But according to a 2006 analysis by University of Nottingham researcher David Gardner, winning times at major races like the Kentucky Derby and the Epsom Derby have remained stagnant since about 1950. Over the same period, winning times at major marathons such as the Olympics continued to drop by more than 15 percent.20

Run a lot of miles Some faster than your race pace Rest once in a while22

If I could go back in time to alter the course of my own running career, after a decade of writing about the latest research in endurance training, the single biggest piece of advice I would give to my doubt-filled younger self would be to pursue motivational self-talk training—with diligence and no snickering.